13 research outputs found
Nanosized Chevrel phases for dendrite-free zincâion based energy storage: unraveling the phase transformations
The nanoscale form of the Chevrel phase, MoS, is demonstrated to be a highly efficient zinc-free anode in aqueous zinc ion hybrid supercapacitors (ZIHSCs). The unique morphological characteristics of the material when its dimensions approach the nanoscale result in fast zinc intercalation kinetics that surpass the ion transport rate reported for some of the most promising materials, such as TiS and TiSe. In situ Raman spectroscopy, post-mortem X-ray diffraction, Hard X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations were combined to understand the overall mechanism of the zinc ion (de)intercalation process. The previously unknown formation of the sulfur-deficient ZnMoS (ZnMoS) phase is identified, leading to a re-evaluation of the mechanism of the (de)intercalation process. A full cell comprised of an activated carbon (YEC-8A) positive electrode delivers a cell capacity of 38 mA h g and an energy density of 43.8 W h kg at a specific current density of 0.2 A g. The excellent cycling stability of the device is demonstrated for up to 8000 cycles at 3 A g with a coulombic efficiency close to 100%. Post-mortem microscopic studies reveal the absence of dendrite formation at the nanosized MoS anode, in stark contrast to the state-of-the-art zinc electrode
Formation and reduction of anodic film on polycrystalline Bi electrode in pure methanol solutions
The processes of film formation and reduction of bismuth in pure methanol are phenomenologically studied by means of cyclic voltammetry, ac voltammetry and electrochemical impedance spectroscopy methods. Film formation takes place under low electrode potentials within the potential range from -0.1 to about 0.2 V vs. Ag|AgCl resulting in the development of Bi(CH3O)ads layer. The scan rate effect on the anodic current profile is interpreted in terms of a gradual variation of uncompensated resistance, accompanying the processes of film formation and reduction. Phase sensitive ac voltammetry measurements suggest leaky insulating character of a thin anodic film in agreement with the results of electrochemical impedance experiments
Electrowetting on Glassy Carbon substrates
The wetting properties of carbon surfaces are important for a number of applications, including in electrochemistry. An under-studied area is the electrowetting properties of carbon materials, namely the sensitivity of wetting to an applied potential. In this work we explore the electrowetting behaviour of glassy carbon substrates and compare and contrast the observed response with our previous work using highly oriented pyrolytic graphite. As with the graphite substrate, âwater-in-saltâ electrolytes are found to suppress Faradaic processes, thereby enlarging the electrochemical potential window. A notable difference response to positive and negative polarity was seen for the graphite and glassy carbon substrates. Moreover, whereas graphite has previously been shown to give a reversible electrowetting response over many cycles, an irreversible wetting was observed for glassy carbon. Similarly, the timescales of the wetting process were much faster on the graphitic substrate. Reasons underlying these marked changes in behaviour on the different carbon surfaces are suggested. <br/
Anion Intercalation into Graphite Drives Surface Wetting
The unique layered
structure of graphite with its tunable interlayer
distance establishes almost ideal conditions for the accommodation
of ions into its structure. The smooth and chemically inert nature
of the graphite surface also means that it is an ideal substrate for
electrowetting. Here, we combine these two unique properties of this
material by demonstrating the significant effect of anion intercalation
on the electrowetting response of graphitic surfaces in contact with
concentrated aqueous and organic electrolytes as well as ionic liquids.
The structural changes during intercalation/deintercalation were probed
using in situ Raman spectroscopy, and the results were used to provide
insights into the influence of intercalation staging on the rate and
reversibility of electrowetting. We show, by tuning the size of the
intercalant and the stage of intercalation, that a fully reversible
electrowetting response can be attained. The approach is extended
to the development of biphasic (oil/water) systems that exhibit a
fully reproducible electrowetting response with a near-zero voltage
threshold and unprecedented contact angle variations of more than
120° within a potential window of less than 2 V
Nanocubes of Mo6S8 Chevrel Phase as Active Electrode Material for Aqueous Lithium-Ion Batteries
The development of intrinsically safe and environmentally sustainable energy storage devices is a significant challenge. Recent advances in aqueous rechargeable lithium-ion batteries (ARLIBs) have made considerable steps in this direction. In parallel to the ongoing progress in the design of aqueous electrolytes that expand the electrochemically stable potential window, the design of negative electrode materials exhibiting large capacity and low intercalation potential attracts great research interest. Herein, we report the synthesis of high purity nanoscale Chevrel Phase (CP) Mo 6S 8via a simple, efficient and controllable molecular precursor approach with significantly decreased energy consumption compared to the conventional approaches. Physical characterization of the obtained product confirms the successful formation of CP-Mo 6S 8 and reveals that it is crystalline nanostructured in nature. Due to their unique structural characteristics, the Mo 6S 8 nanocubes exhibit fast kinetics in a 21 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a result of the shorter Li + ion diffusion distance. Full battery cells comprised of Mo 6S 8 and LiMn 2O 4 as negative and positive electrode materials, respectively, operate at 2.23 V delivering a high energy density of 85 W h kg â1 (calculated on the total mass of active materials) under 0.2 C-rate. At 4 C, the coulombic efficiency (CE) is determined to be 99% increasing to near 100% at certain cycles. Post-mortem physical characterization demonstrates that the Mo 6S 8 anode maintained its crystallinity, thereby exhibiting outstanding cycling stability. The cell outperforms the commonly used vanadium-based (VO 2 (B), V 2O 5) or (NASICON)-type LiTi 2(PO 4) 3 anodes, highlighting the promising character of the nanoscale CP-Mo 6S 8 as a highly efficient anode material. In summary, the proposed synthetic strategy is expected to stimulate novel research towards the widespread application of CP-based materials in various aqueous and non-aqueous energy storage systems.</p
The effect of the Nb concentration on the corrosion resistance of nitrogen-containing multicomponent TiZrTaNb-based films in acidic environments
Multicomponent as well as high-entropy-based nitrides have received increasing interest in the field of materials science and engineering. The structural characteristics of these compounds result in a mix of covalent, metallic, and ionic bonds that give rise to a number of attractive properties including high hardness, electrical and thermal conductivities as well as chemical stability. These properties render these materials promising candidates for various industrial applications involving harsh operating conditions. Herein, the corrosion resistances of dc magnetron sputtered nitrogen-containing TiZrTaNby thin films with Nb content ranging from 8.0 to 24.5 at% have been investigated to provide insights regarding the corrosion resistances of multicomponent systems containing more than one passive element. The corrosion resistances and anodic behavior of the films were examined by electrochemical means in 0.1 M H2SO4 and 0.1 M HCl solutions. The results demonstrate that despite the significant differences in the concentration of one of the two main passive elements in the films i.e., Nb, the corrosion resistance did not differ significantly between the films. To provide insights into this phenomenon, the surface chemical state and composition of the prepared films were probed using X-ray photoelectron spectroscopy. It was shown that all samples exhibited Ta-rich surfaces after positive polarization up to 3.0 V vs. Ag/AgCl (3 M NaCl) as a result of the anodic dissolution of Zr and Ti. The thickness of the oxide layer formed upon different anodic polarization was studied using transmission electron microscopy, while complementary electrochemical impedance studies were performed. The extent of Nb dissolution from the surface of the films was, on the other hand, found to be small. These findings highlight the dominant role of Ta in the passivation of the films and demonstrate the minor effect of Nb concentration on the corrosion resistances of the films. However, it was demonstrated that the presence of Nb was still important for the corrosion resistance of the films above 1.4 V vs. Ag/AgCl (3 M NaCl), when replacing Nb with Cr, due to transpassive dissolution of Cr. These results facilitate the design of highly corrosion resistant multicomponent nitrides containing more than one passive element
Taming Electrowetting Using Highly Concentrated Aqueous Solutions
Wetting of carbon surfaces is one of the most widespread,
yet poorly
understood, physical phenomena. Control over wetting properties underpins
the operation of aqueous energy-storage devices and carbon-based filtration
systems. Electrowetting, the variation in the contact angle with an
applied potential, is the most straightforward way of introducing
control over wetting. Here, we study electrowetting directly on graphitic
surfaces with the use of aqueous electrolytes to show that reversible
control of wetting can be achieved and quantitatively understood using
models of the interfacial capacitance. We manifest that the use of
highly concentrated aqueous electrolytes induces a fully symmetric
and reversible wetting behavior without degradation of the substrate
within the unprecedented potential window of 2.8 V. We demonstrate
where the classical âYoungâLippmannâ models apply,
and break down, and discuss reasons for the latter, establishing relations
among the applied bias, the electrolyte concentration, and the resultant
contact angle. The approach is extended to electrowetting at the liquid|liquid
interface, where a concentrated aqueous electrolyte drives reversibly
the electrowetting response of an insulating organic phase with a
significantly decreased potential threshold. In summary, this study
highlights the beneficial effect of highly concentrated aqueous electrolytes
on the electrowettability of carbon surfaces, being directly related
to the performance of carbon-based aqueous energy-storage systems
and electronic and microfluidic devices
Taming Electrowetting Using Highly Concentrated Aqueous Solutions
Wetting of carbon surfaces is one of the most widespread,
yet poorly
understood, physical phenomena. Control over wetting properties underpins
the operation of aqueous energy-storage devices and carbon-based filtration
systems. Electrowetting, the variation in the contact angle with an
applied potential, is the most straightforward way of introducing
control over wetting. Here, we study electrowetting directly on graphitic
surfaces with the use of aqueous electrolytes to show that reversible
control of wetting can be achieved and quantitatively understood using
models of the interfacial capacitance. We manifest that the use of
highly concentrated aqueous electrolytes induces a fully symmetric
and reversible wetting behavior without degradation of the substrate
within the unprecedented potential window of 2.8 V. We demonstrate
where the classical âYoungâLippmannâ models apply,
and break down, and discuss reasons for the latter, establishing relations
among the applied bias, the electrolyte concentration, and the resultant
contact angle. The approach is extended to electrowetting at the liquid|liquid
interface, where a concentrated aqueous electrolyte drives reversibly
the electrowetting response of an insulating organic phase with a
significantly decreased potential threshold. In summary, this study
highlights the beneficial effect of highly concentrated aqueous electrolytes
on the electrowettability of carbon surfaces, being directly related
to the performance of carbon-based aqueous energy-storage systems
and electronic and microfluidic devices
Taming Electrowetting Using Highly Concentrated Aqueous Solutions
Wetting of carbon surfaces is one of the most widespread,
yet poorly
understood, physical phenomena. Control over wetting properties underpins
the operation of aqueous energy-storage devices and carbon-based filtration
systems. Electrowetting, the variation in the contact angle with an
applied potential, is the most straightforward way of introducing
control over wetting. Here, we study electrowetting directly on graphitic
surfaces with the use of aqueous electrolytes to show that reversible
control of wetting can be achieved and quantitatively understood using
models of the interfacial capacitance. We manifest that the use of
highly concentrated aqueous electrolytes induces a fully symmetric
and reversible wetting behavior without degradation of the substrate
within the unprecedented potential window of 2.8 V. We demonstrate
where the classical âYoungâLippmannâ models apply,
and break down, and discuss reasons for the latter, establishing relations
among the applied bias, the electrolyte concentration, and the resultant
contact angle. The approach is extended to electrowetting at the liquid|liquid
interface, where a concentrated aqueous electrolyte drives reversibly
the electrowetting response of an insulating organic phase with a
significantly decreased potential threshold. In summary, this study
highlights the beneficial effect of highly concentrated aqueous electrolytes
on the electrowettability of carbon surfaces, being directly related
to the performance of carbon-based aqueous energy-storage systems
and electronic and microfluidic devices